Neo4j CQL
Neo4j CQL Write Clauses
- Neo4j - Foreach Clause
- Neo4j - Remove Clause
- Neo4j - Delete Clause
- Neo4j - Set Clause
- Neo4j - Merge Command
Neo4j CQL Read Clause
Neo4j CQL General Clauses
- Neo4j - Unwind Clause
- Neo4j - With Clause
- Neo4j - Skip Clause
- Neo4j - Limit Clause
- Neo4j - Order By Clause
- Neo4j - Return Clause
Neo4j CQL Functions
Neo4j CQL Admin
Neo4j Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
Neo4j - Create Unique Constraint
In Neo4j database, CQL CREATE command always creates a new node or relationship which means even though you use the same values, it inserts a new row. As per our apppcation requirements for some nodes or relationships, we have to avoid this duppcation. For this, we should use some database constraints to create a rule on one or more properties of a node or relationship.
Like SQL, Neo4j database also supports UNIQUE constraint on node or relationship properties. UNIQUE constraint is used to avoid duppcate records and to enforce data integrity rule.
Create UNIQUE Constraint
Neo4j CQL provides "CREATE CONSTRAINT" command to create unique constraints on node or relationship properties.
Syntax
Following is the syntax to create a UNIQUE constraint in Neo4j.
MATCH (root {name: "Dhawan"}) CREATE UNIQUE (root)-[:LOVES]-(someone) RETURN someone
Example
Before proceeding with the example, create 4 nodes as shown below.
CREATE(Dhawan:player{id:001, name: "shikar Dhawan", YOB: 1995, POB: "Delhi"}) CREATE(Jonathan:player {id:002, name: "Jonathan Trott", YOB: 1981, POB: "CapeTown"}) CREATE(Sangakkara:player {id:003, name: "Kumar Sangakkara", YOB: 1977, POB: "Matale"}) CREATE(Rohit:player {id:004, name: "Rohit Sharma", YOB: 1987, POB: "Nagpur"}) CREATE(Virat:player {id:005, name: "Virat Kohp", YOB: 1988, POB: "Delhi"})
Following is a sample Cypher Query to create a UNIQUE constraint on the property id using Neo4j.
CREATE CONSTRAINT ON (n:player) ASSERT n.id IS UNIQUE
To execute the above query, carry out the following steps −
Step 1 − Open the Neo4j desktop App and start the Neo4j Server. Open the built-in browser app of Neo4j using the URL http://localhost:7474/ as shown in the following screenshot.
Step 2 − Copy and paste the desired query in the dollar prompt and press the play button (to execute the query) highpghted in the following screenshot.
Result
On executing, you will get the following result.
Verification
Now, try to add another node with a redundant id value. Here, we are trying to create a node with id 002.
CREATE (Jadeja:player {id:002, name: "Ravindra Jadeja", YOB: 1988, POB: "NavagamGhed"})
If you execute this query, you will get an error message as shown in the following screenshot.
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